Method for transmitting/receiving synchronizing signal in wireless communication system and device therefor

ABSTRACT

The present invention relates to a wireless communication system. The method whereby a terminal receives a synchronizing signal in a wireless communication system according to one embodiment of the present invention may comprise the steps of: receiving location information on a domain, from which the synchronizing signal is transmitted, among domains resulting from the division of the whole system bandwidth into N parts along a frequency axis and into M parts along a time axis (wherein N and M are natural numbers); and receiving the synchronizing signal from the domain corresponding to the location information.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is the National Stage filing under 35 U.S.C. 371 ofInternational Application No. PCT/KR2013/009887, filed on Nov. 4, 2013,which claims the benefit of U.S. Provisional Application No. 61/722,226,filed on Nov. 4, 2012 and 61/722,228, filed on Nov. 4, 2012, thecontents of which are all hereby incorporated by reference herein intheir entirety.

TECHNICAL FIELD

The present invention relates to a wireless communication system and,more particularly, to a method of transmitting and receiving asynchronization signal in a wireless communication system, and anapparatus therefor.

BACKGROUND ART

A wireless communication system has been widely developed to providevarious types of communication services such as voice, data, etc. Ingeneral, the wireless communication system is a multiple access systemcapable of supporting communication with multiple users by sharingavailable system resources (bandwidth, transmission power, etc.).Examples of the multiple access system include a code division multipleaccess (CDMA) system, a frequency division multiple access (FDMA)system, a time division multiple access (TDMA) system, an orthogonalfrequency division multiple access (OFDMA) system, a single carrierfrequency division multiple access (SC-FDMA) system, a multi-carrierfrequency division multiple access (MC-FDMA) system, etc.

DISCLOSURE Technical Problem

An object of the present invention devised to solve the problem lies ina method of transmitting and receiving a synchronization signal in awireless communication system, and an apparatus therefor.

Technical problems to be solved by the present invention are not limitedto the above-mentioned technical problems, and other technical problemsnot mentioned herein may be clearly understood by those skilled in theart from description below.

Technical Solution

The object of the present invention can be achieved by providing amethod of receiving a synchronization signal by a terminal in a wirelesscommunication system, the method including receiving locationinformation on a domain, from which the synchronization signal istransmitted, among domains obtained by dividing a whole system bandwidthinto N parts along a frequency axis and into M parts along a time axis(wherein the numbers N and M are natural numbers), and receiving thesynchronization signal from the domain corresponding to the locationinformation.

In another aspect of the present invention, provided herein is a methodof transmitting a synchronization signal by a base station in a wirelesscommunication system, the method including transmitting locationinformation on a domain, from which the synchronization signal istransmitted, among domains obtained by dividing a whole system bandwidthinto N parts along a frequency axis and into M parts along a time axis(wherein the numbers N and M are natural numbers), and transmitting thesynchronization signal from the domain corresponding to the locationinformation.

In another aspect of the present invention, provided herein is aterminal receiving a synchronization signal in a wireless communicationsystem, including a radio frequency (RF) unit, and a processor, whereinthe processor is configured to receive location information on a domain,from which the synchronization signal is transmitted, among domainsobtained by dividing a whole system bandwidth into N parts along afrequency axis and into M parts along a time axis (wherein the numbers Nand M are natural numbers), and receive the synchronization signal fromthe domain corresponding to the location information.

In another aspect of the present invention, provided herein is a basestation transmitting a synchronization signal in a wirelesscommunication system, including an RF unit, and a processor, wherein theprocessor is configured to transmit location information on a domain,from which the synchronization signal is transmitted, among domainsobtained by dividing a whole system bandwidth into N parts along afrequency axis and into M parts along a time axis (wherein the numbers Nand M are natural numbers), and transmit the synchronization signal fromthe domain corresponding to the location information.

Items below may be commonly applied to embodiments of the presentinvention.

The synchronization signals transmitted from different base stations maybe transmitted from domains having different frequency and timeresources.

The synchronization signals transmitted from base stations which providedifferent types of services may be transmitted from domains havingdifferent frequency and time resources.

The number N may be determined based on a value obtained by normalizingtransmission power of a base station connected to the terminal.

The number N may be set to a maximum size of fast Fourier transform(FFT).

The number N may be set to the number of subcarriers included in thewhole system bandwidth.

Advantageous Effects

According to embodiments of the present invention, it is possible tomore effectively transmit and receive a synchronization signal in awireless communication system.

Effects that may be obtained from the present invention are not limitedto the above-mentioned effects, and other effects not mentioned hereinmay be clearly understood by those skilled in the art from descriptionbelow.

DESCRIPTION OF DRAWINGS

The accompanying drawings, which are included to provide a furtherunderstanding of the invention, illustrate embodiments of the inventionand together with the description serve to explain the principle of theinvention.

FIG. 1 is a diagram illustrating an example of a distributed antennasystem (DAS).

FIG. 2 is a diagram illustrating a concept of a base transceiver station(BTS) hotel of the DAS.

FIG. 3 is a diagram illustrating an example of a structure of a radioframe.

FIG. 4 is a diagram illustrating an example of a frequency bandwidth oflegacy communication and a frequency bandwidth of a small cell.

FIG. 5 is a diagram illustrating a first embodiment of allocating asynchronization signal in a communication system according to thepresent invention.

FIG. 6 is a diagram illustrating a second embodiment of dividing a wholesystem bandwidth into N parts in the communication system according tothe present invention.

FIG. 7 is a diagram illustrating a third embodiment of dividing a systemband based on both time and frequency in the communication systemaccording to the present invention.

FIG. 8 is a diagram illustrating a fourth embodiment of allocating asynchronization signal based on inter-cell interference in thecommunication system according to the present invention.

FIG. 9 is a diagram illustrating a fifth embodiment of allocatingdifferent resources to respective carriers of multiple carriers in thecommunication system according to the present invention.

FIG. 10 is a diagram illustrating an example of dividing andtransmitting a synchronization sequence in the communication systemaccording to the present invention.

FIG. 11 is a block diagram illustrating an example of a base station anda terminal applicable to an embodiment of the present invention.

BEST MODE

The embodiments described below correspond to predetermined combinationsof elements and characteristics of the present invention. Moreover,unless mentioned otherwise, the respective elements and characteristicsmay be considered optional features of the present invention. Herein,each element or characteristic of the present invention may also beoperated or performed without being combined with other elements orcharacteristics of the present invention. Alternatively, the embodimentof the present invention may be realized by combining some of theelements and/or characteristics of the present invention. Additionally,the order of operations described according to the embodiment of thepresent invention may be varied. Furthermore, part of the configurationor characteristics of any one specific embodiment of the presentinvention may also be included in another embodiment of the presentinvention, or part of the configuration or characteristics of any oneembodiment of the present invention may replace the respectiveconfigurations or characteristics of another embodiment of the presentinvention.

In this specification, embodiments of the present invention will bedescribed by centering on a relation between data transmission andreception between a base station and a terminal. Here, the base stationserves as a terminal node of a network which directly communicates withthe terminal. In this document, a specific operation described as beingperformed by the base station may be performed by an upper node of thebase station in some cases.

In other words, in a network including a plurality of network nodesincluding the base station, it is clear that various operationsperformed for communication with the terminal may be performed by thebase station or other network nodes than the base station. The term“base station (BS)” may be replaced by the terms fixed station, Node B,eNode B, access point (AP), etc. The term “repeater” may be replaced bythe terms relay node (RN), relay station (RS), etc. In addition, theterm “terminal” may be replaced by the terms user equipment (UE), mobilestation (MS), mobile subscriber station (MSS), subscriber station (SS),etc.

The specific terms used in the following description of the presentinvention are provided to facilitate the understanding of the presentinvention. Therefore, without deviating from the technical spirit of thepresent invention, such specific terms may also be changed to otherterms.

In some cases, in order to avoid any ambiguity in the concept of thepresent invention, some known structures and devices may be omitted, orthe present invention may be illustrated in the form of a block diagramfocusing on the essential functions of each structure and device.Furthermore, throughout the entire description of the present invention,the same reference numerals will be used for the same elements of thepresent invention.

The embodiments of the present invention may be supported by at leastone the disclosed standard documents for wireless access systemsincluding Institute of Electrical and Electronics Engineers (IEEE) 802,3rd generation partnership project (3GPP), 3GPP long term evolution(LTE), LTE-advanced (LTE-A), and 3GPP2. In other words, among theembodiments of the present invention, partial operation steps orstructures of the present invention, which have been omitted from thedescription of the present invention in order to clarify the technicalspirit of the present invention may also be supported by theabove-described standard documents. Furthermore, the terms disclosed inthe description of the present invention may be described based upon theabove-mentioned standard documents.

The technology described below may be used in a wide range of wirelessaccess systems, such as code division multiple access (CDMA), frequencydivision multiple access (FDMA), time division multiple access (TDMA),orthogonal frequency division multiple access (OFDMA), single carrierfrequency division multiple access (SC-FDMA), etc. CDMA may be realizedby radio technology such as universal terrestrial radio access (UTRA) orCDMA2000. TDMA may be realized by radio technology such as global systemfor mobile communications (GSM)/general packet radio service(GPRS)/enhanced data rates for GSM evolution (EDGE). OFDMA may berealized by a radio technology such as IEEE 802.11 (Wi-Fi), IEEE 802.16(WiMAX), IEEE 802-20, evolved UTRA (E-UTRA), etc. UTRA corresponds to aportion of the universal mobile telecommunications system (UMTS). As aportion of evolved UMTS (E-UMTS) using E-UTRA, the 3GPP LTE systemadopts OFDMA on downlink and adopts SC-FDMA on uplink. LTE-A has evolvedfrom 3GPP LTE. WiMAX may be described based upon the IEEE 802.16estandard (WirelessMAN-OFDMA Reference System) and the evolved IEEE802.16m standard (WirelessMAN-OFDMA Advanced system). For clarity, inthe description of the present invention, the present invention will bedescribed based upon 3GPP LTE and 3GPP LTE-A. Nevertheless, thetechnical spirit of the present invention is not limited to 3GPP LTE and3GPP LTE-A.

A distributed antenna system (DAS) will be described with reference toFIG. 1.

In a current wireless communication environment, the amount of datarequired has rapidly increased due to introduction of Machine-to-Machine(M2M) communication and proliferation of various devices such as asmartphone, a tablet PC, etc., which require high data transmissioncapacities. To satisfy demand for large data capacity, communicationtechnology is being developed toward a carrier aggregation (CA)technology for efficient use of more frequency bands, multi-antenna andcoordinated multi-point technologies for increasing a data capacitywithin a limited frequency, etc. A communication environment is evolvingtoward increasing the density of APs accessible to users. An AP mayincrease a data capacity through several APs having small coverage areassuch as a Wi-Fi AP, a cellular femto AP, a cellular pico AP, etc. inaddition to a cellular macro AP. The AP may take the form of a remoteradio head (RRH), an antenna node of the DAS, etc.

Unlike a centralized antenna system (CAS) in which antennas of basestations (BS, base transceiver station (BTS), Node-B, and eNode-B) areclose to each other at a center of a cell, the DAS manages antennasdistributed in various positions in a cell by a single base station. TheDAS is distinguished from a femto/pico cell in that several antennanodes form one cell. Initially, the DAS has been used to further installantennas in order to cover a shadow area. However, the DAS may beregarded as a type of multiple-input multiple-output (MIMO) system inthat base station antennas may support one or several users bysimultaneously transmitting and receiving several data streams. The MIMOsystem is regarded as an essential for satisfying a requirement of nextgeneration communication due to high frequency efficiency (spectralefficiency). For the MIMO system, the DAS is advantageous over the CASin terms of high power efficiency obtained when a distance between auser and an antenna decreases, a high channel capacity due to lowcorrelation between base station antennas and low interference,communication performance having a relatively uniform qualityirrespective of a location of a user in a cell, etc.

FIG. 1 illustrates an example of the DAS. As illustrated in FIG. 1, theDAS includes a base station and antenna nodes (a group, a cluster, etc.)connected to the base station. An antenna node is connected to the basestation by wire or wirelessly. In addition, the antenna node may includeone or a plurality of antennas. In general, antennas included in oneantenna node are spaced apart from each other by several meters orfarther and regionally included in the same spot. The antenna nodefunctions as an access point accessible by a terminal. In an existingDAS, the antenna node is identified with or is not distinguished fromthe antenna. However, a relation between the antenna node and theantenna needs to be clearly defined to operate the DAS.

FIG. 2 illustrates a concept of a BTS hotel of the DAS. Referring toFIG. 2, in an existing cellular system, one BTS controls three sectors,and each base station is connected to a base station controller(BSC)/radio network controller (RNC) through a backbone network.However, in the DAS, base stations connected to each antenna node may begathered in one place (BTS hotel). In this way, it is possible to reducecosts for land and building for installation of the base stations, andto maintain and manage the base stations at one place. In addition, itis possible to greatly increase a backhaul capacity by installing theBTS and a mobile switching center (MSC)/BSC/RNC at one place.

A structure of a radio frame will be described with reference to FIG. 3.

In a cellular OFDM radio packet communication system, uplink/downlinkdata packet transmission is performed in subframe units, and oncesubframe is defined as a predetermined time period (or time section)including multiple OFDM symbols. The 3GPP LTE standard supports a Type 1radio frame structure, which is applicable to FDD (Frequency DivisionDuplex), and a Type 2 radio frame structure, which is applicable to TDD(Time Division Duplex).

(a) of FIG. 3 illustrates an exemplary structure of a type 1 radioframe. A downlink radio (or wireless) frame is configured of 10subframes, and one subframe is configured of 2 slots in a time domain.The time consumed (or taken) for one subframe to be transmitted isreferred to as a TTI (transmission time interval). For example, thelength of one subframe may be equal to 1 ms, and the length of one slotmay be equal to 0.5 ms. One slot includes a plurality of OFDM(orthogonal frequency division multiplexing) symbols in the time domainand includes a plurality of Resource Blocks (RBs) in the frequencydomain. Since the 3GPP LTE uses the OFDMA in a downlink, an OFDM symbolis used to indicate one symbol section. The OFDM symbol may also bereferred to as an SC-FDMA symbol or a symbol section. As a resourceallocation unit, a Resource Block (RB) may include a plurality ofconsecutive subcarriers in one slot.

The number of OFDM symbols included in one slot may vary depending uponthe configuration of a CP (Cyclic Prefix). The CP may be divided into anextended CP and a normal CP. For example, in case the OFDM symbol isconfigured of a normal CP, the number of OFDM symbols included in oneslot may be equal to 7. And, in case the OFDM symbol is configured of anextended CP, since the length of an OFDM symbol is increased, the numberof OFDM symbols included in one slot becomes smaller than when the OFDMsymbol is configured of a normal CP. In case of the extended CP, forexample, the number of OFDM symbols included in one slot may be equal to6. In case the user equipment is moving at high speed, or in case thechannel status is unstable, the extended CP may be used in order tofurther reduce the interference between the symbols.

In case of using the normal CP, since one slot includes 7 OFDM symbols,one subframe includes 14 OFDM symbols. At this point, the first maximumof 3 OFDM symbols of each subframe are allocated to a PDCCH (physicaldownlink control channel), and the remaining OFDM symbols may beallocated to a PDSCH (physical downlink shared channel).

(b) of FIG. 3 illustrates an exemplary structure of a type 2 radioframe. The type 2 radio frame consists of 2 half frames, and each halfframe is configured of 5 general subframes and a DwPTS (Downlink PilotTime Slot), a Guard Period (GP), and a UpPTS (Uplink Pilot Time Slot),wherein 1 subframe is configured of 2 slots. The DwPTS is used forperforming initial cell search, synchronization or channel estimation inthe user equipment. And, the UpPTS is used for matching a channelestimation performed in the based station with an uplink transmissionsynchronization performed in the user equipment. The guard period refersto a period for eliminating (or removing) interference that occurs in anuplink, due to a multiple path delay of a downlink signal between anuplink and a downlink.

The structure of the radio frame is merely an example. The number ofsubframes included in a radio frame, the number of slots included in asubframe, or the number of symbols included in a slot may be variouslychanged.

FIG. 4 illustrates an example of a frequency bandwidth of legacycommunication and a frequency bandwidth of a small cell.

A concept of a local area is introduced to satisfy a large amount ofdata transfer of next generation communication. In other words, localarea access corresponding to a new cell deployment is required toreinforce service support for each user.

FIG. 4 illustrates a concept of a small cell according to the new celldeployment. In other words, a network may configure and operate a widesystem band in a band having a high center frequency rather than afrequency band operated in a legacy LTE system for a terminal. Inaddition, it is possible to support basic cell coverage based on acontrol signal such as system information through an existing cellularband, and maximize transmission efficiency using a wider frequency bandin a small cell of a high frequency. Therefore, local area access istargeted to a terminal having low-to-medium mobility located in arelatively small area. A distance between the terminal and the basestation may be set to a smaller cell of hundreds of meters than anexisting cell of several kilometers.

In such cell, the distance between the terminal and the base stationdecreases, and a high-frequency band is used. Thus, channelcharacteristics below may be expected.

Delay spread: As the distance between the base station and the terminaldecreases, delay of a signal may decrease.

Subcarrier spacing: When an OFDM-based frame similar to LTE is applied,an allocated frequency band is great, and thus a value may be set to anextremely large value which is greater than existing 15 KHz.

Doppler frequency: A high Doppler frequency occurs in a high-frequencyband when compared to a low frequency band, and thus coherent time maybe dramatically shortened.

This specification proposes a scheme of transmitting a synchronizationsignal for high-frequency band transmission, and describes variousembodiments based on characteristics of the high-frequency band.

In general, delay spread of a channel decreases in a high-frequency bandin which a carrier frequency is 5 GHz or more. In addition, in thehigh-frequency band, path loss of the channel greatly increases, andthus stable performance may be ensured when a distance to the basestation is short. Therefore, it is preferable to use a smaller cellstructure in communication using the high-frequency band when comparedto existing cellular communication, and use OFDM corresponding to amultiple access scheme for resource utilization and ease of control.

When the channel characteristic is considered, an existingsynchronization signal based on a single symbol/single sequence such asin LTE may not provide sufficient performance. Therefore, hereinafter, adescription will be given of considerations for transmission of thesynchronization signal in the high-frequency band.

First, increase in center frequency of a service band needs to beconsidered.

A center frequency band of 5 GHz or more or several GHz or more may beused instead of a channel environment of 5 GHz or less in which theexisting cellular system or a Wi-Fi system is operates because anavailable wide frequency band may not be ensured around 2 GHz. Afrequency band used for existing communication entails difficulties inalteration of use and utilization due to several restrictions.

Second, a wide system bandwidth is required.

Next generation communication is required to support not only anexisting full high definition (HD)-based service but also an ultradefinition (UD)-class service or more. Therefore, a service needs to beprovided using a wider bandwidth in order to support a high transferrate. Here, when a service is provided using a bandwidth of hundreds ofMHz or more or several GHz or more, it is inefficient to transmit thesynchronization signal in a whole frequency band because powerconsumption is great when the synchronization signal is transmitted in awhole widened system bandwidth.

Lastly, high-density cell deployment based on a small cell is required.

High-density deployment of a small cell is efficient in high-frequencyband communication. This scheme is the most efficient scheme forsupporting a high transfer rate, and may maximize a capacity of theentire system through denser cell deployment. However, when thesynchronization signal is transmitted in a band of several GHz in asmall cell in which transmission power of the base station is low,quality of the synchronization signal received by the terminal may bedegraded, and thus performance of acquiring synchronization may bedegraded.

Hereinafter, embodiments below will be proposed based on the threecharacteristics of high-frequency band communication.

First Embodiment

According to a first embodiment of the present invention, a base stationmay transmit a synchronization signal in a part of a system bandwidth ofhigh-frequency band communication. However, a location of thesynchronization signal is not restricted to a middle point of the systembandwidth, that is, a domain on which a direct current (DC) subcarrieris transmitted.

FIG. 5 illustrates the first embodiment in which the synchronizationsignal is allocated in a high-frequency band communication system.

Referring to FIG. 5, a location from which the synchronization signal isallocated may be a middle point of a whole system bandwidth and beshifted to another domain. The synchronization signal is transmittedwith high power when compared to a general data signal so as to beeasily detected. Therefore, the synchronization signal may interferewith or be interfered by a terminal that accesses a particular basestation. In this case, a transmission domain of the synchronizationsignal may be changed differently between base stations.

The base station may transmit information about a location from whichthe synchronization signal is transmitted. For example, informationabout a location of a synchronization signal of a secondary cell may betransmitted through radio resource control (RRC) signaling of a primarycell in a system that supports CA. When the location of thesynchronization signal is transmitted as bitmap information, a locationof a synchronization signal channel may be indicated by the number ofsubcarriers, that is, ┌log₂ N_(FFT)┐. When a size of fast Fouriertransform (FFT) is 1024, a total of 10 bits is required. In astand-alone system, the terminal may perform blind search to detect allcandidates for the synchronization signal in a whole band.

Second Embodiment

According to a second embodiment, a base station may transmit asynchronization signal in a plurality of domains obtained by dividing awhole frequency band.

FIG. 6 illustrates the second embodiment in which the whole frequencyband is divided into N bands in a communication system according to thepresent invention.

Referring to FIG. 6, the whole frequency band is divided into N domains(N being a natural number). In this instance, the base station maytransmit the synchronization signal by selecting one domain or M (1≦M≦N)domains among the divided domains.

An object of a high-frequency band communication system is to acquire ahigh transfer rate using a wide system bandwidth. In this instance, whenthe synchronization signal is transmitted in the whole frequency band, aterminal needs to detect the synchronization signal in the wholefrequency band without a filtering process. As a result, complexity ofthe terminal increases, and the synchronization signal may not berapidly detected.

Therefore, according to the second embodiment of the present invention,a frequency band is divided into N domains, and the synchronizationsignal is transmitted in M domains corresponding to a part of thedivided domains, thereby allowing the terminal to rapidly detect thesynchronization signal. When complexity of the terminal is not greatlyaffected, the synchronization signal may be transmitted in a whole bandby setting M to N. The number N of the divided bands may be set to amaximum size of FFT or the number of available subcarriers. A maximumvalue of N corresponds to the number of divided bands obtained bydividing the whole frequency band using a subcarrier as a unit. Inaddition, N may be determined according to a level of normalizedtransmission power. The number N of the divided frequency bands may betransmitted to the terminal through RRC signaling.

A location from which the synchronization signal is transmitted may betransmitted as bitmap information. When the number N of the dividedfrequency bands is 10, information about the location from which thesynchronization signal is transmitted may be configured as Table 1 bysetting ┌log₂ N┐ to 4 bits.

TABLE 1 Location of synchronization signal Bit information 0 0000 1 00012 0010 3 0011 4 0100 5 0101 6 0110 7 0111 8 1000 9 1001

In addition, Table 2 may be configured by a one-to-one correspondencebetween frequency bands and 10 respective bits in total.

TABLE 2 Location of synchronization signal Bit information 0 00000000001 0000000010 2 0000000100 3 0000001000 4 0000010000 5 0000100000 60001000000 7 0010000000 8 0100000000 9 1000000000

The location from which the synchronization signal is transmitted may bepredefined or transmitted to the terminal through RRC signaling, etc.Alternatively, the terminal may detect the synchronization signalthrough blind search. The information about the location from which thesynchronization signal is transmitted may be transmitted or blind searchmay be determined based on processing capability and complexity of theterminal or a channel environment factor such as interference, etc. Forexample, in a system that supports CA, information about a location of asynchronization signal of a secondary cell may be transmitted throughRRC signaling of a primary cell.

Third Embodiment

FIG. 7 illustrates a third embodiment in which a whole system bandwidthis divided based on time and frequency and a synchronization signal istransmitted in a divided domain.

Referring to FIG. 7, various combinations may be created using atime-frequency pattern. In the second embodiment, a frequency domain isdivided on a constant time domain. However, according to the thirdembodiment, the system band may be divided based both on time andfrequency.

For example, when the whole system bandwidth is divided into N frequencydomains, and M symbols are used to transmit the synchronization signalin a time domain (here, N and M being natural numbers), the total numberof combinations may be expressed by Equation 1 below. In this instance,the M of symbols for transmission of the synchronization signal may becontiguous or noncontiguous in the time domain. FIG. 7 illustrates acase in which a frequency domain is divided into four domains and foursymbols are selected in the time domain.

The number of bands selected in the frequency domain: N_(f)=Σ_(n=1) ^(N)_(N)C_(n)

The number of symbols selected in the time domain: N_(t)=Σ_(m=1) ^(M)_(M)C_(m)

The number of candidates for a whole band on which the synchronizationsignal is transmitted: N_(f)×N_(t)

Information about a location from which the synchronization signal istransmitted may be transmitted as bitmap information after indexingcoordinate information or a whole domain. Alternatively, the informationabout the location from which the synchronization signal is transmittedmay be transmitted to a terminal through RRC signaling, etc. orpredefined. Alternatively, the terminal may detect the synchronizationsignal through blind search. The information about the location fromwhich the synchronization signal is transmitted may be transmitted orblind search may be determined based on processing capability andcomplexity of the terminal or a channel environment factor such asinterference, etc. For example, in a system that supports CA,information about a location of a synchronization signal of a secondarycell may be transmitted through RRC signaling of a primary cell.

Fourth Embodiment

As described in the foregoing, a high-frequency band communicationsystem is expected to use high-density cell deployment based on a smallcell. In this case, when all base stations transmit synchronizationsignals in the same time-frequency domain, synchronization signalsincluding different sequences may greatly interfere with each other.This may cause an error when a terminal acquires initial synchronizationand acquires neighbor cell synchronization such as handover, etc.Therefore, the fourth embodiment of the present invention describes amethod of configuring a synchronization signal differently between basestations based on an interference condition of the terminal. The methodof configuring the synchronization signal in different time-frequencydomain resources for respective base stations may be predefined orperformed through RRC signaling.

For example, when service coverage areas of adjacent small cells overlapunder a circumstance in which various networks are included in a servicecoverage area of the terminal as in FIG. 8, the synchronization signalmay be transmitted through different domains for respective basestations by managing the networks. In this way, it is possible togreatly reduce interference occurring between synchronization signals inhigh-density deployment of the small cells. In addition, a resourceallocation pattern of the synchronization signal may be changed byupdating interference condition information of each cell. Further, thisconcept may be applied by varying resource allocation depending onservice type of a base station (macro, pico, femto, RRH, relay, hotspot,etc.).

Fifth Embodiment

A fifth embodiment of the present invention describes a method oftransmitting synchronization signals on different time-frequencyresource domains for respective carriers in a system using multiplecarriers.

A next generation communication system may employ a multi-carrieroperation scheme using aggregated bands having a certain size or more inaddition to a single broadband. An available bandwidth is restricted foreach center frequency band, and thus it is difficult to allocate abandwidth of several GHz or more at a time. Therefore, it is preferableto construct a system based on multiple carriers by joining bands havinga certain size or more.

Examples of the system based on multiple carriers may include an LTE-Asystem. The LTE-A system employs CA technology to aggregate and transmita plurality of component carriers, thereby enhancing a transmissionbandwidth of a terminal and increasing frequency use efficiency. TheLTE-A system may extend a bandwidth up to 100 MHz by simultaneouslyusing a plurality of carriers (multiple carriers) together rather than asingle carrier which has been used in LTE rel 8/9. In other words, acarrier, which has been defined as a maximum of 20 MHz in legacy LTE rel8/9, is redefined as a component carrier, and one terminal is allowed touse a maximum of five component carriers through the CA technology.

Currently, the CA technology mainly has characteristics below.

(1) Aggregation of contiguous component carriers is supported, andaggregation of noncontiguous component carriers is supported.

(2) The number of carrier aggregations may be different between uplinkand downlink. When the technology needs to be compatible with anexisting system, uplink and downlink need to configure the same numberof component carriers.

(3) Different transmission bandwidths may be acquired by configuringdifferent numbers of component carriers between uplink and downlink.

(4) For a terminal, each component carrier independently transmits onetransport block, and has an independent hybrid automatic repeat request(HARQ) mechanism.

Unlike a legacy LTE system using one component carrier, CA which uses aplurality of component carriers requires a method of effectivelymanaging the component carriers. To efficiently manage the componentcarriers, the component carriers may be classified according tofunctions and characteristics. The component carriers may be classifiedinto a primary component carrier (PCC) and secondary component carriers(SCCs). The PCC functions as a core component carrier for management ofcomponent carriers when several component carriers are used, and one PCCis defined for each terminal.

In addition, other component carriers except for the one PCC are definedas the SCCs. The PCC may function as a core carrier that manages allaggregated component carriers, and the other SCCs may function asadditional frequency resource providers to provide a high transfer rate.For example, a base station may perform connection (RRC connection) forsignaling with respect to a terminal through the PCC. Security andinformation for an upper layer may be provided through the PCC. Inreality, when only one component carrier is present, the componentcarrier may correspond to the PCC. In this instance, the componentcarrier may function similarly to a carrier of the legacy LTE system.

The fifth embodiment of the present invention describes a method oftransmitting synchronization signals through different time-frequencydomains for respective carriers in a system using multiple carriers.

First, different frequency bands are allocated for respective carriersbased on one base station, and other base stations are configured suchthat allocated patterns do not overlap or overlap at a particulardistance or more. In this way, it is possible to greatly decrease apossibility that synchronization signal interference occurs between basestations.

For example, as shown in Table 3, when the number of candidates for atime-frequency domain is four (N=4), the number of multiple carriers isthree (M=3), and the number of overlapping base stations is four (L=4),combinations below may be created.

TABLE 3 Synchronizing Multiple carriers signal resource F1 band F2 bandF3 band Base station 1 Index 0 Index 1 Index 2 Base station 2 Index 1Index 2 Index 3 Base station 3 Index 2 Index 3 Index 0 Base station 4Index 3 Index 0 Index 1

FIG. 9 illustrates an example of synchronization signal allocationaccording to the fifth embodiment of the present invention and, moreparticularly, illustrates synchronization signal allocation according toTable 3. Referring to FIG. 9, it can be understood that four partialbands in total are present in a frequency band, and 0 to 3 are supportedas resource allocation indices.

Information about a location from which a synchronization signal istransmitted may be transmitted to a terminal through RRC signaling, etc.or predefined. Alternatively, the terminal may detect thesynchronization signal through blind search. The information about thelocation from which the synchronization signal is transmitted may betransmitted or blind search may be determined based on processingcapability and complexity of the terminal or a channel environmentfactor such as interference, etc. For example, in a system that supportsCA, information about a location of a synchronization signal of asecondary cell may be transmitted through RRC signaling of a primarycell.

Sixth Embodiment

The first to fifth embodiments define resources for transmission ofsynchronization signals. The sixth embodiment defines an actuallytransmitted synchronization signal, that is, a sequence when afrequency-time resource for transmission of a synchronization signal isdetermined.

According to the first to third embodiments, a synchronization signalmay be transmitted in some of domains obtained by dividing a wholesystem bandwidth with respect to frequency or time. Here, basically, thesame synchronization sequence may be actually mapped to the respectivedomains. However, it is possible to configure different synchronizationsequences for the respective domains. In addition, when differentsynchronization sequences are configured for the respective domains, onesynchronization sequence having a length of the whole frequency band maybe designed, and then the synchronization sequence may be divided andtransmitted according to lengths of the respective domains asillustrated in FIG. 10.

Base Station and Terminal to which an Embodiment of the PresentInvention May be Applied

FIG. 11 illustrates a base station 110 and a terminal 120 to which anembodiment of the present invention may be applied.

When a relay is included in a wireless communication system,communication is performed between the base station 110 and the relay ina backhaul link, and communication is performed between the relay andthe terminal 120 in an access link. Therefore, the base station 110 orthe terminal 120 illustrated in the figure may be replaced by the relayas needed.

Referring to FIG. 11, the wireless communication system includes thebase station 110 and the terminal (or UE) 120. The base station 110includes a processor 112, a memory 114, and a radio frequency (RF) unit116. The processor 112 may be configured to implement a procedure and/ora method proposed by the present invention. The memory 114 is connectedto the processor 112 to store various information associated with anoperation of the processor 112. The RF unit 116 is connected to theprocessor 112 to transmit and/or receive a radio signal. The terminal120 includes a processor 122, a memory 124, and an RF unit 126. Theprocessor 122 may be configured to implement a procedure and/or a methodproposed by the present invention. The memory 124 is connected to theprocessor 122 to store various information associated with an operationof the processor 122. The RF unit 126 is connected to the processor 122to transmit and/or receive a radio signal. The base station 110 and/orthe terminal 120 may have a single antenna or multiple antennas.

The embodiments of the present invention described above arecombinations of elements and features of the present invention. Theelements or features may be considered selective unless otherwisementioned. Each element or feature may be practiced without beingcombined with other elements or features. Further, an embodiment of thepresent invention may be constructed by combining parts of the elementsand/or features. Operation orders described in embodiments of thepresent invention may be rearranged. Some elements or features of anyone embodiment may be included in another embodiment and may be replacedwith corresponding elements or features of another embodiment. It isobvious to those skilled in the art that claims that are not explicitlycited in each other in the appended claims may be presented incombination as an embodiment of the present invention or included as anew claim by subsequent amendment after the application is filed.

A particular operation described as being performed by a base station inthis document may be performed by an upper node thereof in some cases.In other words, it is obvious that various operations performed forcommunication with a terminal in a network which includes a plurality ofnetwork nodes including a base station may be performed by the basestation or other network nodes other than the base station. The term“base station” may be replaced by the terms fixed station, Node B, eNodeB (eNB), an AP, etc.

The embodiments of the present invention may be achieved by variousmeans, for example, hardware, firmware, software, or a combinationthereof. In a hardware configuration, an embodiment of the presentinvention may be achieved by one or more Application Specific IntegratedCircuits (ASICs), Digital Signal Processors (DSPs), Digital SignalProcessing Devices (DSPDs), Programmable Logic Devices (PLDs), FieldProgrammable Gate Arrays (FPGAs), processors, controllers,microcontrollers, microprocessors, etc.

In a firmware or software configuration, an embodiment of the presentinvention may be implemented in the form of a module, a procedure, afunction, etc. performing a function or an operation described above.Software code may be stored in a memory unit and executed by aprocessor.

The memory unit may be located inside of the processor or outsidethereof to transmit and receive data to and from the processor viavarious known means.

Those skilled in the art will appreciate that the present invention maybe carried out in other specific ways than those set forth hereinwithout departing from the spirit and essential characteristics of thepresent invention. The above embodiments are therefore to be construedin all aspects as illustrative and not restrictive. The scope of theinvention should be determined by the appended claims and their legalequivalents, not by the above description, and all changes coming withinthe meaning and equivalency range of the appended claims are intended tobe embraced therein.

INDUSTRIAL APPLICABILITY

The present invention is applicable to a wireless communication devicesuch as a terminal, a relay, a base station, etc.

The invention claimed is:
 1. A method of receiving a synchronization signal by a terminal in a wireless communication system, the method comprising: receiving location information on a domain, through which the synchronization signal is transmitted, among domains obtained by dividing a whole system bandwidth into N parts along a frequency axis and into M parts along a time axis; and receiving the synchronization signal through the domain corresponding to the location information, wherein the numbers N and M are natural numbers and the number N is determined based on a value obtained by normalizing transmission power of a base station connected to the terminal.
 2. The method according to claim 1, wherein synchronization signals transmitted from different base stations are transmitted through domains having different frequency and time resources.
 3. The method according to claim 1, wherein synchronization signals transmitted from base stations which provide different types of services are transmitted through domains having different frequency and time resources.
 4. The method according to claim 1, wherein the number N is set to a maximum size of fast Fourier transform (FFT).
 5. The method according to claim 1, wherein the number N is set to the number of subcarriers included in the whole system bandwidth.
 6. A method of transmitting a synchronization signal by a base station in a wireless communication system, the method comprising: transmitting location information on a domain, through which the synchronization signal is transmitted, among domains obtained by dividing a whole system bandwidth into N parts along a frequency axis and into M parts along a time axis; and transmitting the synchronization signal through the domain corresponding to the location information, wherein the numbers N and M are natural numbers and the number N is determined based on a value obtained by normalizing transmission power of a base station connected to the terminal.
 7. The method according to claim 6, wherein synchronization signals transmitted from different base stations are transmitted through domains having different frequency and time resources.
 8. The method according to claim 6, wherein synchronization signals transmitted from base stations which provide different types of services are transmitted through domains having different frequency and time resources.
 9. The method according to claim 6, wherein the number N is set to a maximum size of FFT.
 10. The method according to claim 6, wherein the number N is set to the number of subcarriers included in the whole system bandwidth.
 11. A terminal receiving a synchronization signal in a wireless communication system, the terminal comprising: a radio frequency (RF) unit; and a processor, wherein the processor is configured to control the RF unit to receive location information on a domain, through which the synchronization signal is transmitted, among domains obtained by dividing a whole system bandwidth into N parts along a frequency axis and into M parts along a time axis, and receive the synchronization signal through the domain corresponding to the location information, wherein the numbers N and M are natural numbers and the number N is determined based on a value obtained by normalizing transmission power of a base station connected to the terminal.
 12. A base station transmitting a synchronization signal in a wireless communication system, the base station comprising: an radio frequency (RF) unit; and a processor, wherein the processor is configured to control the RF unit to transmit location information on a domain, through which the synchronization signal is transmitted, among domains obtained by dividing a whole system bandwidth into N parts along a frequency axis and into M parts along a time axis, and transmit the synchronization signal through the domain corresponding to the location information, wherein the numbers N and M are natural numbers and the number N is determined based on a value obtained by normalizing transmission power of a base station connected to the terminal. 